1. Field of the Invention
This invention relates to apparatus providing for private viewing of information displayed on the LCD screen of a notebook or laptop computer, and, more particularly, to a filtering device extending in front of an LCD screen, having an active mode in which a limitation is placed on the viewing angle through which data on the screen can be read and an inactive mode, in which the screen can be viewed normally.
2. Background Art
Laptop or notebook computers are often used in crowded, public places such as airplanes for writing personal or otherwise confidential information. Under such circumstances, there is generally a concern the a nearby person, such as the person in the next airplane seat, may be reading sensitive material. This concern keeps many people from using a laptop computer in many instances when its use would be particularly convenient. If the computer is used in this way, sensitive data may be stolen.
Privacy can be provided during the use of a laptop computer by restricting the viewing angle through which the screen may be viewed, so that only the person sitting directly in front of the screen can read the data written on it. This angle can be limited by holding a privacy screen across the front of the computer display screen, so that the display screen can only be viewed through the privacy screen.
FIG. 1 is a fragmentary cross-sectional view of a first type of privacy screen 10 placed in front of a computer display screen 12. The privacy screen 10 includes a number of partitions 14 separated by transparent light channels 16. The partitions 14 limit the angle at which light is transmitted through the privacy screen 10 to the angle indicated by the reference numeral 18. When a portion of the screen is viewed from outside this angle, it appears to be dark. If the partitions 14 extend only vertically, the angle of view is limited from side to side, so that a person sitting next the person using the computer is prevented from reading the data on the screen. If the partitions 14 extend horizontally, as well as vertically, the angle of view is also limited vertically, so that a person standing behind the person sitting and using the computer is also prevented from reading the data on the screen. An example of a privacy screen having closely-spaced partitions or louvers is sold by the 3M Company as a PF14.1 Notebook Privacy Filter.
The partitions may be small louvers, ridges, or other shapes. A number of examples from the patent literature describe ways of making and using films including such shapes. For example, U.S. Pat. No. 4,766,023 describes a louvered plastic film that can be more easily handled and installed by coating at least one surface with a solvent-free monomer composition and exposing the coating to ultraviolet radiation to polymerize the coating. U.S. Pat. No. 4,764,410 describes such a film in which the coating is polymerized to an adhesive state, preferably forming a pressure-sensitive adhesive. U.S. Pat. No. 4,812,702 describes a privacy screen using a pair of films with small louvers, placed against one another so that the image from a color CRT must pass through both the films. The louvers of each of the films are tilted in opposite directions at angles from the vertical, substantially reducing any visual Moire patterns resulting from an interaction between the pixels on the CRT screen and the louvers. U.S. Pat. No. 5,528,319 describes a privacy filter having two or more aligned and spaced-apart grids, each of which includes a array of strips blocking light transmission. U.S. Pat. No. 5,993,940 describes a composite including a polymeric film having a first generally planar major surface and an opposite second major surface defined by a multiplicity of elongate parallel contiguous ridge portions, each of which has a generally triangular cross section. The film can provide visual transmission between its first major surface and its second major surface, while coatings along obscured portions of the second major surface prevent viewing of visual images through the film.
The patents referenced above do not describe a means for selectively providing the effect of the louvers or partitions. Such means for selectively providing is particularly desirable in the application of a method for achieving privacy in the use of a notebook computer, since such a device is typically used both in public places, such as airplanes and waiting rooms, requiring such privacy, and in more private places, where there is no need for such privacy. In such more private places, a failure to cancel the effect of the louvers or partitions means that the notebook computer is unnecessarily difficult to use, first because the privacy film covering the screen of the computer absorbs a significant portion of the light used to form the image visible on the screen, and second because it is often more difficult to use a computer when the screen has a narrow angle of view. In particular, what is needed is a convenient way to move a louvered privacy filter into place in front of the LCD screen of a notebook computer for use in a situation requiring privacy, and to move the louvered privacy filter out of place to be stored within the notebook computer for use in a situation not requiring privacy.
One method for varying the angle through which an LCD screen may be viewed is described in U.S. Pat. No. 6,211,930, which describes variable viewing angle LCD systems for use in automatic teller machines where, during parts of a transaction, it is desirable that information on the screen can be read only by the person using the machine and standing directly in front of the screen. The system includes conventional elements for backlighting a transmission type LCD screen, with such conventional backlighting elements including a reflector, a light source, and an optional brightness enhancer. A collimator and a variable diffuser are interposed between these conventional backlighting elements and the LCD screen. The collimator consists of a pair of louver films through which light passes only in essentially straight lines. The variable diffuser, which can be switched between a transparent state and a scattering state by the application of an electric field, may be a polymer dispersed liquid crystal cell or reverse mode polymer stabilized collisteric texture cell. When the variable diffuser is in its transparent state, the light passing through the LCD screen remains collimated, so that the screen is only visible over a narrow viewing angle. When the variable diffuser is set to scatter the collimated light, light passes through the LCD screen at a range of angles, so a large angle of viewing is made available.
What is needed is a method for varying the angle of view without requiring the illumination for wide angles to be first collimated and then scattered. The process of collimating absorbs much of the illumination, in the form of light not passing through the louvers in essentially straight lines. Then, for wide angle viewing, the light is scattered by the diffuser, lowering the peak level of illumination at a viewing angle perpendicular to the screen.
FIG. 2 is a fragmentary cross-sectional view of a second type of privacy screen 20 placed in front of a liquid crystal display (LCD) screen 22. This privacy screen 20 is a polarizing film, which takes advantage of the fact that the light output of the LCD 22, is strongly polarized. The LCD screen 22 is of a conventional type, including a light source 26, such as a flourescent light; a diffuser 27, which directs light from the light source in the outward direction of arrow 28; an inner polarizing filter 30; a liquid crystal panel 32 including liquid crystal material 34, extending between a pair of glass plates 36; and an outer polarizing filter 38. Light emitted by the light source 26 is polarized by the inner polarizing filter in a first direction, forming a plane polarized area of illumination passing through the liquid crystal panel 32 and through the outer polarizing filter 38, which is aligned to pass light polarized in this direction.
The liquid crystal panel 32 is capable of forming cross-polarized images against this plane polarized background light. For example, the liquid crystal material 34 comprises mesomorphic crystals which align themselves with an electric field. When these crystals are aligned in this way, polarized light passing through them is rotated into a condition of cross-polarization with the outer polarizing filter 38, so that the light is absorbed by the outer polarizing filter 38. When the electric field is removed, the alignment of the crystals returns to a random state, so that polarized light passes through the liquid crystal panel 32 without this rotation. Thus, with the electric field removed the plane polarized light passes through the liquid crystal panel 32, retaining this plane polarization, and thus also passes through the outer polarizing filter 38. The glass plates 36 include embedded electrodes, which are selectively driven to produce an electric field forming alphanumeric characters and graphics. A color display is formed by including patterns of red, green, and blue dots within the light path to form colored pixels. The angle through which the image formed by the liquid crystal panel 32 may be effectively viewed is limited by imposing a polarizing privacy filter 20 between the outer polarizing filter 38 and the viewer (not shown). The polarizing privacy filter 20 is aligned to be partially cross-polarizing with the plane polarized light transmitted through the liquid crystal panel 32 without rotation. While the polarizing privacy filter 38 darkens the illuminated areas of the displayed information, even when the image is viewed from a direction indicated by line 42, perpendicular to the plane of the liquid crystal panel 32, this darkening effect resulting from interposing the polarizing privacy filter 38 is much greater when the image is viewed from an oblique angle, as indicated by line 44. Thus, the effective viewing angle of the displayed image is substantially reduced. U.S. Pat. No. 5,488,496 describes this kind of privacy filter in configurations in which at least one of the polarizers associated with creating a cross-polarized image on a liquid crystal display is displaceable. One of these configurations includes cylindrical rollers extending above and below an LCD, with a clear, transparent continuous belt made from a material such as acetate film being tensioned between the rollers. The polarizing privacy filter is constructed on one region of the belt, with this region being the height and width of the LCD. This privacy filter is moved into position between the LCD and the view, and subsequently out of this position, by rotation of one of the rollers using a crank or an electric motor.
What is needed is a method for moving a privacy filter between a position in which it is hidden and a position in which it extends in front of the LCD of a notebook computer without a need to attach the privacy filter to a transparent belt. Such a method would eliminate a need to establish a belt tracking system and would eliminate covering the LCD with a plastic sheet even when the privacy filter is moved away from the LCD screen.
Another method for achieving privacy when viewing a computer screen is to provide opaque members extending outward from the sides and top of the screen, as described in U.S. Pat. Nos. 4,444,465, 5,717,566, and 5,877,896. While this method has the additional advantage of minimizing glare on the computer screen, and can be used entirely to control glare, it is of limited use in crowded conditions such as airplanes because of the bulkiness of the associated devices.
Screens have also been described as being used to reduce glare when viewing cathode ray tube (CRT) displays, including television sets. U.S. Pat. No. 4,819,085 describes a protective screen formed of a frame and a series of woven, non-metallic fibers, which is fitted over a display surface of a CRT to reduce glare and/or to diffuse emanated radiation and static electricity. U.S. Pat. No. 4,633,322 describes a filter, composed of a woven micromesh screen, held in front of a the CRT screen of a television set, and removed from the CRT by being rolled onto a roller when the television set is not being used to prevent an accumulation of dust in the filter mesh.
What is needed is a mechanism providing for a conveniently removed privacy filter composed of, for example, a louvered film.
Accordingly, an objective of the invention is to provide apparatus for a notebook computer in which a privacy filter, limiting the angle at which the display screen can be viewed, is readily made effective and ineffective;
Another objective of the invention is to provide a privacy filter which is easily brought into place in front of the display screen of a notebook computer for use in situations requiring privacy and moved into a storage cavity within the notebook computer for use in situations not requiring privacy;
According to a first aspect of the invention, display apparatus for a computing system is provided, including a display panel, a display cover, and a privacy filter. The display panel includes a display surface and causes a visible image to be produced on said display surface in response to electrical signals generated within said computing system. The display cover, which extends around said display panel, includes a window outwardly exposing said display surface and a cavity extending from a first end of said window to a closed end of said cavity. The privacy filter, which includes a filter sheet, is movable between a closed position with said filter sheet extending to cover said display surface and an open position exposing said display surface through said window. A first portion of said privacy filter in said open and closed positions extends into said cavity. The filter sheet limits a viewing angle through which said visible image is discernible.
The display apparatus may additionally include a roll rotatably mounted within said cavity, with a first end of said privacy filter being attached to a peripheral surface of said roll. Rotating said roll in a first direction wraps an increasing portion of said privacy filter around said roll, moving said privacy filter from said closed position to said open position, and rotating said roll opposite said first direction unwraps an increasing portion of said privacy filter from said roll, moving said privacy filter from said open position to said closed position.
Alternately, the cavity may include a rear cavity portion extending along a side of said display panel opposite said display surface, with the display apparatus additionally including a curved deflector deflecting a portion of said privacy filter into said rear cavity portion as said privacy filter is moved from said open position into said closed position.
According to a second aspect of the invention, display apparatus for a computing system is provided, including a display panel, a liquid crystal device, and an external polarizer. The display panel, which includes a display surface, causes a visible image to be produced on said display surface. The visual image includes darkened areas and illuminated areas having light polarized in a first plane. The liquid crystal device extends externally across said display surface, with the display surface being visible through said liquid crystal device. The external polarizer extends externally across said liquid crystal device, which is electrically switchable between a first mode causing light from said illuminated areas to be cross-polarized with said polarizer and a second mode causing light from said illuminated areas to be plane polarized with said external polarizer.